Friday nights without Jonathan Ross will leave a gaping hole in BBC1's weekend schedule, even if it returns after Ross serves his three-month suspension, but it will also deprive celebrities of a valuable vehicle for selling their wares. Ross's show, which regularly attracts 2.5 million viewers, despite being screened at 10.35pm, has become the favoured outlet for stars with a film to publicise or a book to promote, and PRs and agents who had booked their clients on to the programme will be frantically redrawing their media strategies following the BBC's decision to suspend Ross over the Andrew Sachs affair.

Should Ross leave the BBC, plenty of broadcasters will be willing to match his reputed £6m a year salary to snap him up, such is his reputation as the UK's chat show king. A flamboyant figure who began as a humble researcher, Ross used his own fame to attract the biggest names to his show, but, in common with other programmes, guests do not always take their place on his sofa for the kudos and commercial upside an appearance can generate. Like rivals on other channels, Friday Night with Jonathan Ross has been known to pay guests, a revelation that may surprise viewers who assume entertainers traipse the talk show circuit because they need the publicity rather than a boost to their bank balance.

The show's success means it only pays out as a last resort - its market-leading position means big American stars contractually obliged to publicise the films they star in tend to appear as a matter of routine when they are in London on the European leg of their promotional tour.

But the explosion of entertainment programmes that rely on high-profile guests to deliver big ratings has created a market in celebrity appearances, as they vie to attract the biggest names in an intensely competitive field.

'It's always been the case,' says a leading celebrity PR, 'that you can get paid for Richard & Judy. You can get paid for anything. If you've got nothing to promote, you can get good money because you're not doing any other show or newspaper interviews. It becomes an exclusive. Rates vary from £10,000 to £20,000, and '£40,000 if you're lucky'.

Another PR who represents entertainment figures with global appeal says Hollywood stars such as Tom Cruise routinely command as much as £30,000 to appear on chat shows, although the scramble for A-list guests is slightly less frenetic since Michael Parkinson's show disappeared from ITV. Parkinson complained in his recent biography that his show, cancelled by ITV earlier this year, suffered because it could not match the £15,000 fees guests and their agents were negotiating with rival talk shows.

Graham Norton, who moved from Channel 4 to BBC2 after the corporation secured his services in another multi-million-pound deal, also imported a practice of paying some big stars to appear on the programme, according to industry insiders. Goldie Hawn, a recent guest, is thought to have been paid tens of thousands of pounds, and other US stars without a film to promote are also often paid.

'Guest budgets vary in size, and are used differently by production companies,' says one industry source. 'Some shows might not pay anything for six months and then blow it all on a few big stars at the end of the series.' Even Top Gear, BBC2's flagship car programme, has been known to pay guests to appear, according to leading PR advisers.

The amount depends on the fame of the guest and their news value. Public figures who have questions to answer but nothing to promote can command a premium, not least because the rules of engagement are different when money changes hands. They can expect a rough ride at the hand of their interlocutors, and, without a product to plug, the conversation is more likely to turn to controversial topics they might not otherwise agree to discuss. Norton, in particular, is treated warily by many showbiz agents because his appeal depends in part on poking fun at his guests, and his unpredictable approach sometimes seems calculated to cause maximum discomfort.

'A publicist would be much more reticent to put their client in that sort of environment,' says an insider who has worked on several of Britain's biggest chat shows. Often a substantial fee is the only incentive that will persuade them to submit to the ordeal.

Commercial broadcasters who screen This Morning and Paul O'Grady's C4 show are free to pay whatever it takes in the open market for guests, though many are not superstars and are happy to appear free of charge.

Using licence fee money to hire guests would be more controversial, but crucially the BBC does not make chat shows in-house. Ross and Norton's programmes are made by the entertainers' own production companies, which means that appearance fees, when they are paid, do not come directly from the BBC's coffers.

Ross's show, recorded on Thursday but broadcast late on Friday, can deliver a huge sales boost as viewers head to the shops the morning after it is aired, and its role as a promotional tool means it doesn't have to pay out as often as its rivals. 'A lot of PRs will be staring into their coffee this week,' says a senior industry figure representing several household names.

Many will be desperately trying to shoehorn clients on to shows they previously refused to deal with. The irony is that Ross could command a huge fee himself were he to appear on a rival chat show to discuss the events of last week.